SetAsr I'm concerned about the possibility of any information about my activities being leaked.
Could you be more specific? Are you worried about your activities you on the Google apps? What Google apps in particular? Around using Sandboxed Google Play Services, is it signed in, does it have the network permission? Are you using any Google apps signed into your Google account? In Settings > Passwords, passkeys & accounts are you signed into a Google account, cause if you are you might want to sign out.
See here: https://discuss.grapheneos.org/d/10918-google-account-not-linked-across-google-apps
Or is your concern about the Google apps leaking information about you from other apps/activities?
SetAsr However, according to my logic, without access to the Internet, no data can leak, right?
Not exactly. There's still IPC (inter profile communication) to think about which, if two or more apps agree to communicate with each other, they can share different information (even without internet permission). Though my knowledge on IPC is limited, so other's might know more detail.
Here's a thread related to IPC: https://discuss.grapheneos.org/d/1549-more-questions-about-ipc
Off-topic, but related to concerns about what data apps have access too and what kinds of fingerprinting apps can do: https://discuss.grapheneos.org/d/17118-identifiers-across-private-space-and-profiles/4